Optimized Electronic Modification of S-Doped CuO Induced by Oxidative Reconstruction for Coupling Glycerol Electrooxidation with Hydrogen Evolution

Highlights S-doped CuO nanorod arrays (S-CuO/CF) constructed by sulfur leaching and oxidative remodeling strategy require only 1.23 and 1.33 V versus hydrogen evolution reaction (HER) to provide glycerol oxidation currents of 100 and 500 mA cm−2. S-CuO/CF shows satisfactory performance (at 100 mA cm−2, Vcell = 1.37 V) assembled as the anode in asymmetric coupled electrolytic cell of glycerol oxidation reaction and HER. The study identifies the key factors involved in the GOR reaction pathway, which include the C–C bond breaking and lattice oxygen deintercalation steps. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-023-01159-6.

coated onto carbon paper (CP) (10*10*0.3 mm, HCP030N). The formulation for the coating consists of 0.03 g of Pt/C, 1 g of isopropyl alcohol and 0.5 g of deionized water. It is crucial to ensure that the slurry is effectively dispersed via ultrasonic means before application via spraying.

S1.4 Materials Characterization
The crystal phase of the obtained catalysts was studied via X-ray diffraction (XRD) on a Rigaku D/max-2500pc device with Cu Kα radiation (λ = 1.54 Å). The scanning electron microscope (SEM) (Hitachi S-4800) and Transmission Electron Microscope (TEM) (FEI Tecni G20, 200 kV) were applied to collect the information of morphological and structural information of all samples. The element composition and distribution on catalysts were detected by means of the Energy Dispersive System (EDS) and detected on the Hitachi S-4800. The X-ray photoelectron spectroscopy (XPS) is characterized by a Thermo Fisher Scientific II spectrometer with an Al Kα source (1486.6 eV).

S1.5 Electrochemical Measurements
The catalytic performance of all the catalysts was evaluated in a standard threeelectrode cell configuration on Gamry Reference 1000 electrochemical equipment at room temperature. This process was performed with the Pt foil (10*10 mm), Hg/HgO electrode and catalyst samples (10*10 mm) as the counter electrode, reference electrode, and working electrode, respectively. The OER and GOR performance tests utilized electrolytes of 1 M KOH and 1 M KOH + 0.1 M glycerol, respectively. All 1 M KOH used in this work are pre-saturated with N2. The LSV were gained at same condition with scan rate of 5 mV s -1 with iR correction (Current interruption (CI) compensation). All the potentials vs. Hg/HgO were converted into a standard reversible hydrogen electrode (RHE) by means of the Nernst equation: ERHE = EHg/HgO + 0.0594 pH + 0.098. The cyclic voltammetry (CV) curves were tested at 40, 60, 80, 100, 120 mV s -1 and were used to determine the electrical double-layer capacitances (Cdl). The specific calculation equation is as follows: in which ja and jc is the anodic and cathodic voltammetric current density, respectively, recorded at the middle of the selected potential range, and v is the scan rate.
The electrochemcial active surface area (ECSA) in this work is calculated by the following publicity: in which Cdl, ideal is the double layer capacitance of an ideally flat electrode, which is commonly taken as 40 μF cm -2 in alkaline media.
Electrochemical impedance spectroscopy (EIS) was performed at 1.25 V vs. RHE and the frequency ranges from 10 5 Hz to 0.1 Hz. The stability of the final sample was performed by chronoamperometry (CA).

S1.6 Product Analysis
The oxidation products of glycerol were determined by ion chromatography (IC) with as9-hc column and conductivity detector. A long-term electrolytic reaction of glycerol oxidation was performed at a constant potential of 1.35 V vs. RHE in 200 mL electrolyte of 1 M KOH and 0.1 M glycerol. 0.5 mL electrolyte was extracted every 2 hours and diluted 10 times with deionized water as the solution to be tested. 0.954 g sodium carbonate was dissolved in 1000 mL secondary water as eluent at a constant flow rate of 0.6 mL/min.
The corresponding faradaic efficiencies (FE) toward formate and glycolate are calculated based on the following equations: where and are the final concentrations of formate and glycolate, respectively; V is the volume of the electrolyte solution; F is the Faraday's constant (96485 C/mol); The integration of the j-t response curve (chronoamperometry) yields the Qtotal, representing the total charge transfer.
The Faradaic efficiency calculations of the glycerol oxidation production are based on the following balance half-reactions:

S2 Computational Methods
The density functional theory (DFT) calculations were carried out by CASTEP. The exchange-correlation interaction between atomic cores and valence electrons with DFT was described by generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional. Plane-wave cutoff energy of 500 eV was used in all computations. The total energy and force convergence threshold was set as 2*10 -5 eV/atom and 0.05 eV/Å. A three-layer slab with a p(3×2) supercell was used to simulate the CuO (-111) and S-CuO (-111) surfaces, and the bottom layer was fixed to mimic bulk properties. For surfaces geometry optimization, a Monkhorst-Pack k-point mesh of 2×2×1 was employed. The d-band centers were determined by taking the weighted mean energy of the projected density of states (pDOS) of metal 3d states relative to the Fermi level.

Fig. S24
The cyclic reaction path of S-CuO/CF driven glycerol electrooxidation to prepare formic acid and glycolic acid